Flexible vinyl chloride polymer sheet materials are commonly used in a wide variety of decorative applications including wallcoverings, upholstery and decorative films. It is generally desirable that the exposed surface of the vinyl chloride polymer sheets be provided with a protective, stain-resistant layer which can be easily cleaned without excessive rubbing or excessive use of harsh cleaning solvents. The protective layer should preferably exhibit good abrasion and solvent resistance. The aqueous coating composition should have a long shelf-life and good colloidal stability. For applications wherein a low gloss coating is desired for aesthetic reasons, such as for upholstery, it is highly desirable that flatting agents such as silica are capable of being effectively dispersed or redispersed in the coating composition.
A compounded and plasticized vinyl chloride polymer laminate having an outer adherent and stain resistant layer comprising the crosslinked reaction product of a reactive polyester having free carboxylic acid groups and an alkylated benzoguanamine-, urea- or melamine-formaldehyde resin is disclosed in U.S. Pat. No. 4,603,074.
One shortcoming with the stain resistant layer disclosed by U.S. Pat. No. 4,603,074 is that it is produced by coating a vinyl chloride polymer substrate with a solvent based curable polyester resin system having a high volatile organic compound content (typically 50 percent or more). The volatile organic components of the solvent which are evaporated during drying and curing of the coating must be recovered in order to comply with government regulations relating to chemical emission standards. Because of the problems and expense of solvent recovery and the potential for inadvertent human exposure to solvent vapor, it is highly desirable to provide a curable coating composition having a low volatile organic compound content which upon application to a vinyl chloride polymer substrate and subsequent curing forms an adherent, stain resistant layer of a laminate.
Another disadvantage with the stain resistant layer disclosed by U.S. Pat. No. 4,603,074 is that the ball point and felt tip pen stains cannot be easily removed with ordinary soaps or detergents, but instead often require harsher solvents such as acetone. It is desirable to provide a coating capable of forming a stain resistant layer on a vinyl chloride polymer substrate wherein the removal of frequently encountered stains can be effected without resorting to acetone or other harsh solvents.
U.S. Pat. Nos. 3,996,177 to Ludwig, 4,524,173 to Rehfuss et al., and 4,794,136 to Touhsaent each teach crosslinkable acrylic latex compositions.
Ludwig discloses a latex coating composition for providing hardboard with a hard, water resistant, and chemical resistant coating. The reference teaches that a combination of melamine-formaldehyde and urea-formaldehyde crosslinking agents are needed to achieve good shelf stability and good water resistance. Ludwig is unconcerned with substantially eliminating volatile organic compounds and consistently teaches the addition of substantial amounts of isopropyl alcohol to the disclosed latex coating compositions. Ludwig is also unconcerned with providing polyvinyl chloride substrates with low gloss coatings.
Rehfuss et al. disclose coating compositions for rigid metal or plastic substrates which simultaneously exhibit improved hardness and impact resistance. Rehfuss et al. utilize predominantly nonionic surfactants to allow the use of substantial amounts of acid catalysts to bring the pH of the composition down to the range of 1.0-02. It is disclosed that the low pH is required for rapid, low temperature curing, but makes the composition disadvantageous for use with a full range of substrates, and is therefore preferably used as a topcoat of a two-coat system. Rehfuss et al. teach that the latex polymer must contain from about 4 to about 9 percent by weight of an amide functional monomer to provide stability with the nonionic surfactants which are used. Rehfuss et al. are also unconcerned with providing a low gloss coating for polyvinyl chloride substrates.
Touhsaent teaches an adhesive composition for bonding a polyolefin film to a polyvinylidene chloride film and is completely unconcerned with providing a low gloss topcoat for polyvinyl chloride substrates. Touhsaent specifically teaches the use of chain transfer agents during preparation of the latex polymer which leads to lower molecular weight acrylic polymers which are generally unsuitable as coatings for polyvinyl chloride substrates because of their poor chemical and solvent resistance.